Mechanism for automatic network formation and medium access coordination

ABSTRACT

The invention provides a set of mechanisms by which a wireless mobile mesh node equipped with a directional antenna may self form and self adapt its steady-state communications schedule. A link establishment handshake is carried out over an ongoing subtemplate-based discovery scan. During time not reserved for steady-state communications with previously discovered neighbors, nodes continue to search for an establish links with new neighbors. Initial and subsequent bandwidth allocation protocols may be utilized to allow peer nodes to coordinate communication opportunities between the peer nodes without impacting or having knowledge about reservations for communications with other peers. The link establishment and initial bandwidth allocation protocols may be piggy-backed for readily establishing an initial steady-state schedule with a peer upon link establishment without impact on previous steady state reservations by other nodes or on ongoing link establishment attempts elsewhere.

This application is a continuation of U.S. patent application Ser. No.13/233,612, filed Sep. 15, 2011, titled “Mechanism for Automatic NetworkFormation and Medium Access Coordination”, which is a continuation ofU.S. patent application Ser. No. 11/624,452, filed Jan. 18, 2007, titled“Mechanism for Automatic Network Formation and Medium AccessCoordination.” Each of the above priority applications are incorporatedherein by reference.

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owner to licenseothers on reasonable terms provided for by the terms of contract numberDASG60-02-D-0006 awarded by U.S. Army Space and Missile Defense andcontract number N00421-03-D-0007 awarded by Naval Air Warfare Center AD(Pac).

FIELD OF THE INVENTION

The invention relates generally to forming and maintaining a mobile meshnetwork. More particularly, the invention provides a set of mechanismsby which a directional wireless mobile mesh network may self form andself adapt.

BACKGROUND

The field of mobile mesh networks, often referred to interchangeablywith Mobile Adhoc Networks (MANETs) is attracting increasing interest asa field of research because of their suitability to a variety ofmilitary and commercial applications. Specifically, mesh networks areimportant in settings where telecommunication facilities must beinstalled quickly, as in disaster recovery or in combat, and in areaswhere a large coverage footprint is desirable.

Conventional wireless (e.g., 802.11, 802.16) and cellular networks areinfrastructure-based networks which utilize a hub-and-spoke model(point-to-multipoint topology). In the hub-and-spoke model, all wirelessdevices must be within broadcast range of a central access point (AP) tocommunicate. All data traffic must pass through this point as no twohost devices communicate directly. In addition, mobility is supportedonly by a subset of the nodes (end host devices), while infrastructurenodes are often still assumed to be fixed.

For example, FIG. 1 depicts a hub-and-spoke model (102) which may beused by conventional wireless networks using 802.11 and/or 802.16. In an802.11 environment, an access point (104) may communicate directly witha client station 106. In terms of network formation, to enter a BasicService Set (BSS), client stations (STA) such as client station (106)must obtain synchronization information from access point (104). Thismay be done through one of two methods: (1) Passive scanning—where aclient station waits to hear a beacon packet which is sent periodicallyfrom the access point containing the synchronization information, or (2)Active scanning—where the client station tries to find an access pointby transmitting probe requests and waiting for probe responses from theaccess point. Either method may be chosen according to powerconsumption/performance trade-offs. An authentication exchange mayfollow so a client station (106) may prove its knowledge of a password.Finally, the association process may allow client station (106) andaccess point (104) to become aware of each-other's capabilities. Notuntil this process is complete is the client station (106) capable oftransmitting and receiving data frames.

For coordination of medium access, the 802.11 standard relies on CarrierSense Multiple Access with Collision Avoidance (CSMA/CA) with a randombackoff mechanism. Namely, when a node receives a packet that is to besent, it checks to be sure the channel is clear (no other node istransmitting at the time). If the channel is clear, then the packet issent. If the channel is not clear, the node waits for a randomly chosenperiod of time, and then checks again to see if the channel is clear.This period of time is called the backoff factor, and is counted down bya backoff counter. If the channel is clear when the backoff counterreaches zero, the node re-transmits the packet. If the channel is notclear when the backoff counter reaches zero, the backoff factor is setagain, and the process is repeated. Because the probability that twonodes will choose the same back off factor is small, collisions betweenpackets are minimized. However, transmission of a streamy burst oftraffic by one node may result in temporarily monopolizing the medium atthe cost of all other nodes being held off.

Although conventional wireless networking standards such as 802.11 claimto provide a mesh capability through Independent Basic Service Sets(IBSS), this requires that all nodes be directly connected by virtue ofbeing within omni-directional antenna range from each other, becausetraffic cannot be forwarded, thus restricting network topology. The802.11s proposal is aimed at true mesh networks where nodes now routeinformation. However the 802.11s proposal does not discuss nor tacklemesh networks that use highly directional antennas. The use of highlydirectional antennas improves reach of the network over networks usingomni-directional antennas. However, with the narrower beam of highlydirectional antennas, each node may theoretically communicate with onlyone other node at a time. The nodes must point their respective antennatoward each other. Thus, nodes must assume a schedule in whichcommunications to their neighbors are organized in a way that maximizesmedium sharing but still reduces interference. Specifically, each nodein a set of nodes may communicate simultaneously with another node in amutually exclusive set of nodes. The mechanism for accessing the mediumis referred to as Time Division Pairwise Access (TDPA). Issues ofscheduling brought on by directivity are described as “the antennaproblem” or the “directivity scheduling problem.”

In the 802.11s proposal, medium access is strictly contention-basedthrough use of virtual carrier sensing. Contention-based medium accessapproaches utilize bandwidth and reserved frequency channels merely forsensing the medium and by requiring the reservation of the medium eachtime a node wants to communicate—bandwidth and frequencies that couldotherwise be used for transporting user data. Furthermore, the risk ofmonopolizing the medium remains when a node that is granted the mediumis the source of a large burst of traffic.

The 802.16 standard is another infrastructure-based network thatimplements at least one Subscriber Station (SS) communicating with aBase Station (BS) via a point-to-multipoint air interface. For example,FIG. 1 depicts a hub-and-spoke model (102) which may be used by aconventional wireless 802.16 network. In FIG. 1, subscriber stations(110, 112, 114, and 116) communicate with a Base Station (BS) (108) viaa point-to-multipoint air interface.

The downlink (i.e., the link from the base station (108) to the clientstations) operates on a point-to-multipoint basis. In this sense, themedium is truly shared, much as it is in a wired LAN such as Ethernet.Using sectorized antennas, within a given frequency channel and antennasector, all stations receive the same transmission. The base station(108) is the only transmitter operating in this direction, so ittransmits without having to coordinate with other stations, except forthe overall time division duplexing that may divide time into uplink anddownlink transmission periods. Depending on the class of serviceprovided, subscriber stations (110-116) may be issued continuing rightsto transmit or the right to transmit may be granted by the BS (108)after receipt of a request from the user.

In the 802.16 world, WiMax mesh extensions seem to only address fixedmesh networks with the option to have centralized or distributed slotallocation for TDMA-based scheduling. In the former, slot allocation isdetermined at a single node known as the “Mesh Base Station”—aninfrastructure-based approach, while the latter approach requires thedistribution of schedules to all neighbors since nodes “compete” foravailable slots and must find out when “their bid” is unsuccessful.

In directional mobile mesh (Ad-hoc) networks, highly directionalantennas are used giving the network longer reach than networks usingomni-directional antennas. Each node must “take a turn” to communicatewith each of its neighbors, but a set of nodes can communicatesimultaneously with a mutually exclusive set of nodes.

A legacy approach to network formation involves use of a lengthy andcomplex approach for network formation. In the legacy approach,semi-centralized control, and frequent operator intervention wererequired. Specifically, a single unit was designated as the NetworkControl Unit (NCU) and this unit was commanded to initiate the networkformation process. The NCU conducted a discovery scan by assuming therole of “interrogator” while all other nodes would be placed in the“responder” role. This implied that initially, the NCU conducted adiscovery scan by transmitting a sequence of messages initiating whatcould become multiple instances of a link establishment handshake.

In this 360-degree “Alert” scan, covering n distinct bearings, theinterrogator would transmit an “Alert” message in each direction, andall responders would be “listening” (receiving) in the opposite(reciprocal) direction. This way, whether the scan consisted ofsequential or a predetermined order of bearings to be visited, there wasa 1/n probability that if the interrogator and a responder were withincommunications range of each other, at some point during the scan, theywould “face each other” and the responder would “hear” the interrogator.

The network expanded in this fashion, thus building up the connectivityin phases, where nodes formed concentric rings or levels, each saidlevel executing a different phase of the process. Once no nodes werefound by the nodes at the last level, and the nodes at every levelestimated every other node had learned of the identity of every node andof the network's connectivity (a process referred to as reaching networkclosure), every node would compute a global schedule (a schedule forevery node) that was a function of the network topology and specifictime-late and throughput requirements.

This was based on the premise that because every node had the same inputknowledge, by applying the same algorithm, every node computed the sameschedule. Furthermore, this process required that nodes transition tousing the local portion of this schedule (i.e., the portion of theschedule pertaining to that node and its neighbors) simultaneously anddoing so would also incur large delays that were a function of the worstcase network topology. All this time, nodes were not permitted toexchange user data. The only exchanges constituted link establishmentprotocols and network management knowledge propagation.

Once nodes were participating in steady-state communications via thisTDPA schedule (i.e., nodes had transitioned to the operational state ofthe node and were finally permitted to exchange user data), and as nodeswould move within or beyond communications range of others, links wouldform and/or drop. In addition, a set of acquisition functions wererequired in order to bring additional nodes into the network, or tore-acquire recently lost links. Most of these functions requiredoperator intervention and the resulting changes in connectivity wouldimply the need for recalculation of the global schedule, which in turnimplied another lengthy delay as knowledge about these changes again hadto be propagated to every node in the network prior to the recalculationof a new schedule and eventual transition to it.

The activities taking place in this lengthy process are illustrated inFIG. 2. Image (202) of FIG. 2 shows a central node (204) searching forpeers as an interrogator. Links are established with each discoverednode as shown in image (206). Responding nodes as illustrated in image(208) become interrogators. Previously established links are maintainedon a temporary maintenance schedule. The next levels of links are thenestablished as shown in image (210). In image (212), a new level ofinterrogators may begin searching for peers. A network forms inconcentric rings or levels using temporary schedules until no other peercan be found at the last level encountered. As nodes learn about eachother and determine that unconnected peers are within range, cross linksare established as shown in image (214). Information from every node(identity, position, connectivity, etc.) is propagated until every nodedetermines that it knows about every other node. As shown in image (216)every network node calculates an identical global TDPA schedule andsynchronizes its transition to the local portion of that schedule. Oncenodes begin using their newly computed schedule, lost and newly acquiredlinks trigger a lengthy network-wide propagation of the event and therecalculation of any transition to a new schedule as shown in image(218).

This complex and long process must take place merely for the purpose offorming the network and establishing a schedule, at which time, nodesare finally permitted to begin exchanging user data. Furthermore, anylater changes in network connectivity or link attributes require yetagain, the lengthy network-wide propagation of these changes andsubsequent recalculation of, and transition to, a new global schedule.

Thus, it would be advancement in the art to provide mechanisms forself-forming, self-maintaining a directional mobile mesh network, wheremedium access coordination and adaptation is such that it impacts aminimal number of nodes.

SUMMARY

The following presents a simplified summary in order to provide a basicunderstanding of some aspects of the invention. The summary is not anextensive overview of the invention. It is neither intended to identifykey or critical elements of the invention nor to delineate the scope ofthe invention. The following summary merely presents some concepts ofthe invention in a simplified form as a prelude to the more detaileddescription below.

The invention provides a self-forming, self-maintaining directionalmobile adhoc network. In an aspect of the invention, a linkestablishment handshake is carried out over an ongoing subtemplate-baseddiscovery scan. In an embodiment, during time not reserved forsteady-state communications with previously discovered neighbors, nodescontinue to search for and establish links with new neighbors thusincreasing the number of possible paths resulting in increased aggregatebandwidth.

In an aspect of the invention, link establishment (LE) and the initialbandwidth allocation (IBA) protocols may be piggy-backed for readilyestablishing an initial steady-state schedule with a peer upon linkestablishment.

In another aspect of the invention, a fixed length schedule forsteady-state communications representing each node's pool of availableand currently reserved bandwidth is continually used for peer discoveryand link establishment.

In yet another aspect of the invention, coordination of these schedulesmay take place between a node and a peer as they discover each other,simultaneously and independently from other nodes also coordinatingschedules between them without affecting communications with anypreviously acquired neighbors, without requiring the distribution ofknowledge about any other nodes with which links are being created,without requiring the time-consuming calculation of a schedule based onhaving achieved identical global knowledge at every node, and withoutthe incurred additional delay for transitioning to a newly calculatedschedule. Global network management knowledge (knowledge of networkconnectivity and link attributes) may still be propagated but is nolonger essential for the purpose of network formation/maintenance orschedule calculation.

In a further aspect of the invention, initial and subsequent bandwidthallocation protocols may be utilized to allow peer nodes to coordinatecommunication opportunities between the peer nodes without impacting orhaving knowledge about reservations for communications with other peersor by any node further removed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates prior art conventional wireless networks.

FIG. 2 represents a prior art network formation process.

FIG. 3 illustrates exemplary nodes prior to network formation andsteady-state schedule coordination in accordance with an aspect of theinvention.

FIG. 4 illustrates another diagram depicting exemplary nodes prior tonetwork formation and steady-state schedule coordination in accordancewith an aspect of the invention.

FIG. 5 illustrates exemplary nodes participating in a randomizeddiscovery scan in accordance with an aspect of the invention.

FIG. 6 illustrates a method of receiving a link establishment requestfrom a node in accordance with an aspect of the invention.

FIG. 7 illustrates a method of communicating nodes idle frames inaccordance with an aspect of the invention.

FIG. 8 illustrates selection of common idle frames between two nodes inaccordance with an aspect of the invention.

FIG. 9 illustrates a method of updating steady-state schedules inaccordance with an aspect of the invention.

FIG. 10 illustrates a method of receiving a link establishmenttransmission request in accordance with an aspect of the invention.

FIG. 11 illustrates a method of piggybacking two messages between nodesin accordance with an aspect of the invention.

FIG. 12 illustrates an additional method of selecting idle frames from asteady-state schedule of a node in accordance with an aspect of theinvention.

FIG. 13 illustrates a method of transmitting a link establishmentrequest from a node in accordance with an aspect of the invention

FIG. 14 illustrates another method of receiving a link establishmentrequest from a node in accordance with an aspect of the invention.

FIG. 15 illustrates an additional embodiment in which a nodecommunicates its idle frames in accordance with an aspect of theinvention.

FIG. 16 illustrates an additional embodiment showing selection of commonidle frames between two nodes in accordance with an aspect of theinvention.

FIG. 17 illustrates a method of updating a node's steady-state schedulewithout having to notify or affect any other node in the network inaccordance with an aspect of the invention.

FIG. 18 illustrates a method of searching for additional peers duringidle time in accordance with an aspect of the invention.

FIG. 19 illustrates a continuing process of network formation andsteady-state schedule coordination in accordance with an aspect of theinvention.

FIG. 20 illustrates another node communicating its idle frames inaccordance with an aspect of the invention.

FIG. 21 illustrates a method of selecting common idle frames between thenodes communicated in FIG. 20 in accordance with an aspect of theinvention.

FIG. 22 illustrates a method of updating steady-state schedules based onthe frames selected in FIG. 21 in accordance with an aspect of theinvention.

FIG. 23 illustrates another example of link establishment and initialbandwidth allocation in accordance with an aspect of the invention.

FIG. 24 illustrates a method of transmitting a link establishmentrequest in a first subtemplate in accordance with an aspect of theinvention.

FIG. 25 illustrates a method of receiving a link establishment requestin a first subtemplate in accordance with an aspect of the invention.

FIG. 26 illustrates a method of randomly scheduling frames not reservedfor steady-state communications in accordance with an aspect of theinvention.

FIG. 27 illustrates a method of transmitting a link establishmentresponse and initial bandwidth allocation request in accordance with anaspect of the invention.

FIG. 28 illustrates further processing steady-state schedulescoordination in accordance with an aspect of the invention.

FIG. 29 illustrates an additional method of randomly scheduling framesnot reserved for steady-state communications in accordance with anaspect of the invention.

FIG. 30 illustrates another method of transmitting a link establishmentacknowledgement and initial bandwidth allocation response in accordancewith an aspect of the invention.

FIG. 31 illustrates an established link in accordance with an aspect ofthe invention.

FIG. 32 illustrates a method of participating in additional instances ofhandshake with other discovered peers in accordance with an aspect ofthe invention.

FIG. 33 illustrates nodes prior to network formation and steady-stateschedule coordination in accordance with an aspect of the invention.

FIG. 34 further illustrates nodes prior to network formation andsteady-state schedule coordination in accordance with an aspect of theinvention.

FIG. 35 illustrates nodes participating in a randomized discovery scanin accordance with an aspect of the invention.

FIG. 36 further illustrates nodes prior to network formation andsteady-state schedule coordination in accordance with an aspect of theinvention.

FIG. 37 illustrates receipt of a transmission from a node in accordancewith an aspect of the invention.

FIG. 38 illustrates selecting available response frames among thoseoffered in accordance with an aspect of the invention.

FIG. 39 illustrates completion of messages in accordance with an aspectof the invention.

FIG. 40 illustrates nodes having coordinated their steady statecommunication opportunities between them in accordance with an aspect ofthe invention.

FIG. 41 illustrates further discovery of nodes in accordance with anaspect of the invention.

FIG. 42 illustrates selection of response frames in accordance with anaspect of the invention.

FIG. 43 illustrates the transmission of messages in accordance with anaspect of the invention.

FIG. 44 illustrates the updating of nodes steady state schedules inaccordance with an aspect of the invention.

FIGS. 45-53 illustrate the use of sectorized directional reception andscheduling of the discovery scan in accordance with an aspect of theinvention.

FIGS. 54-58 illustrate adaptive bandwidth allocation among nodes inaccordance with an aspect of the invention.

FIGS. 59-60 illustrate lost link processing among nodes in accordancewith an aspect of the invention.

FIGS. 61-62 illustrate an exemplary configuration of a node inaccordance with an aspect of the invention.

DESCRIPTION Network Formation & Steady-State Schedule Coordination

In an aspect of the invention, rather than having a central nodedesignated as the initiator of network formation, every node may be anequal participant in the process and it merely needs to be powered “on”and configured for the process to automatically begin. For linkestablishment purposes, nodes may randomly assume the interrogator orresponder role, and as two nodes discover each other, they alsocoordinate their steady-state communications per a configured initialbandwidth allocation. The allocation may correspond to the initialreservation of communication opportunities between the two nodes in eachdirection of the link and should correspond to at least the requiredlink maintenance rate (how often a node must receive from a peer inorder to track its position to maintain communications).

Once a short handshake completes, the two nodes become neighbors and mayimmediately transition to use their mutually coordinated steady-statecommunications schedule without dependency or impact on schedulespreviously established with any other peers. Once on steady-statecommunications, two nodes may begin to exchange network traffic. In anaspect of the invention, an initial bandwidth allocation protocol may bepiggy-backed onto the link establishment exchange to quickly beginsteady-state communications.

During time not reserved for steady-state communications with itsneighbors, every node continues to attempt instances of the linkestablishment handshake as it continues to search for additionalpotential neighbors. This takes place, in the greatest extent possiblewithout preemption of previously reserved steady-state communications.In addition, nodes may periodically monitor traffic loads over each oftheir links and may update bandwidth allocations accordingly using asimilar handshake as was used for coordinating the initial allocations.These bandwidth allocation updates may be carried out over the alreadycoordinated steady-state communication opportunities between the twonodes and may result in increasing or decreasing the number ofcommunication opportunities within a steady-state schedule cycle betweenthe two nodes involved.

As a node is powered “on” and becomes operational, the node mayparticipate in a discovery scan. This corresponds to assuming asemi-randomized pattern of communications. Specifically, on each frameof day, the operation to perform (transmission or reception) may beselected by a node randomly, while the direction in which to point is afunction of the frame of day and the selected operation, where frame ofday may be defined as “time of day” in unit of frames. Specifically,each second of a day is further subdivided into a number of frames, sayF, thus there are 24 hours*60 (minutes/hour)*60 (seconds/minute)*F(frames/second)=86400° F. frames in one day. Namely, if on frame f anode randomly chooses to transmit, it will do so in the direction givenby bearing b(f), whereas, a node that is to receive on frame f would doso on its omni-directional antenna for the first portion of the linkestablishment handshake, but for the latter portion, it would point inthe direction given by bearing b(f)+180 degrees (adjusted perhaps fromknowledge of the node's own and its peer's positions). During the scan,the pointing direction covers 360 degrees in equally spaced bearings ina pre-determined order, which may or may not be sequential. The numberof bearings b to cover in a 360-degree scan and by that token, the widthof the increment, may be a configurable resource. The order in whichthese bearings are visited (sequential or not) may be arbitrary butknown uniformly by every node.

Initially, a node may schedule three contiguous sets of frames (orsubtemplates) of s frames each, where s may be at least the amount oftime it takes for a node to “turn around” a received message, i.e., thesum of any inbound delays during reception, and outbound delays duringtransmission. The size of the subtemplates s (in units of frames) may beconfigurable. In “transmit” frames of the first subtemplate, the nodemay transmit the first message in the link establishment handshake.Throughout the handshake, in each transmission requiring the receptionof a subsequent message, the node identifies the “receive” frames withinthe next subtemplate during which the node will be “listening” so thatthe peer node that receives this message may select when to respond.Additionally, in every message, nodes may exchange their positions sothat pointing angles may be computed for pointing the directionalantenna toward a peer.

When a subtemplate boundary is reached, a new subtemplate may berandomly scheduled. The pattern in one subtemplate may be modifiedaccording to received messages in the previous subtemplate aiming atreducing the degree to which a node's steady-state communications arepreempted. As the handshake progresses, nodes may continue to coordinatethe times in which a node will be listening for the next message in thehandshake and in the direction of the peer. By exchanging positioninformation with each message, the link establishment handshake may be asimple three-way handshake, since by the second message, each node knowswhere its peer is located and may thus compute where to point totransmit and listen.

The subtemplate may allow for a node to “look ahead” s frames in advanceand determine randomly scheduled reception opportunities to offer apeer. If none are available due to all being previously reserved forsteady-state communications, as a last recourse, the node overwrites apreviously reserved steady-state communication opportunity withreception operations for the purpose of completing the linkestablishment handshake, thus temporarily preempting some steady-statecommunication opportunities, but not for an extended period of time, asthis would affect only a single subtemplate which may be much shorterthan the minimum maintenance cycle length. Similarly, when a node isoffered a set of “receive” frames by its peer and all of them coincidewith frames the node has already reserved for steady-statecommunications with other peers, the nodes may preempt. Scheduling ofselected frames among those offered by a peer may be done such that anode has sufficient time to process the received frame and to build themessage to be transmitted as a result.

As any two nodes establish a link, they may also coordinate the schedulebetween them. Upon completion of the link establishment handshake, thenodes may immediately transition to using their mutually reservedcommunication opportunities for steady-state communications and beginexchanging data. During time not yet reserved for steady-statecommunications, nodes continue to schedule the random scan patterndescribed for link establishment or complete link establishmenthand-shakes in progress.

By “piggy backing” the link establishment (LE) and the initial bandwidthallocation (IBA) handshakes, steady-state communications schedules maybe coordinated on a link by link basis by two peer nodes as the link isbeing established, without the need to propagate global knowledge andthe need to use multiple temporary schedules used for maintaining a linkuntil a schedule for steady-state communications can be globallycomputed. Additionally, rather than building a steady-state (TDPA)schedule that is of minimum length, in an aspect of the invention, amaximum fixed-length steady-state schedule initially representing a poolfull of idle frames at every node may be used.

The following illustrative example is being used to show various aspectsof the invention and is not meant to be limiting to the scope of theinvention.

FIG. 3 illustrates nodes prior to network formation and steady-stateschedule coordination in accordance with an aspect of the invention. InFIG. 3, a scheduled cycle (302) is depicted for node 1 (304), node 3(306), node 9 (308), and node 11 (310). The schedule cycle (302) for theillustrated nodes begins with a pool (an array) of L idle frames (330),where L is a configurable parameter that may accommodate the worst caseanticipated network topology. L may be based on empirical data, perhapseven starting with a schedule that is in the order of the legacynetwork's maximum schedule length. In an embodiment, L may be the lengthof one steady-state schedule cycle. As a link is established between twonodes, the nodes coordinate the frames within that array during whicheach node may transmit to the peer thus quickly and easily allocatingthe initial bandwidth between them. The initial bandwidth allocation(IBA) handshake may be conducted such that communications over eachdirection of the link are agreed upon without risk of conflictingreservations between a node and its multiple neighbors.

Each node's steady-state communications schedule may be viewed as anarray of frames for communication with each neighbor, which initially,contains only idle frames since a node has yet to form links. The lengthL of this schedule may be configurable and fixed for the entire sessiona system is operational, as is the maintenance cycle length m (i.e.,maximum time in frames required between communications in each directionover a link in order to properly track and point to a neighbor as itmoves, i.e., maintain the link). L may also be validated with respect tob (the number of bearings covered in the discovery scan) so that L isnot a factor or a multiple of b (i.e., b mod L< >0 and L mod b< >0).This may prevent the possibility of neglecting a bearing during thediscovery scan that takes place when a node is conducting steady-statecommunications with at least one neighbor. Thus, L could be validated as

-   -   Repeat    -   If b mod L=0 or L mod b=0, then L=L+1 (or b=b+1, one or the        other) until (b mod L< >0 and L mod b< >0), where,    -   b is the configured number of bearings to be visited during the        discovery scan, and L is the configured steady-state schedule        length.

Once L is validated with respect to b, an initially assumed load d maybe used which corresponds to the minimum number of equally spacedtransmissions that may satisfy the maintenance requirement for aparticular direction of the link in a schedule cycle of the configuredlength L. During the initial bandwidth allocation protocol, each nodemay be assigned a number of frames during which it is to transmit to itsneighbor. As such, during link establishment, this number of framescorresponds to the configured and validated initial load d.

In order to satisfy the maintenance requirement m, it may be seen thatwithin an L-frame schedule cycle, a node may transmit to each of itsneighbors at least ceiling (L/m) times. Ideally, these transmissions maybe staggered in time so that they occur steadily at most every m frames.Namely, the scheduling of multiple transmissions may be such that insearching for the next idle frame to assign each transmission, thestarting point is at most m frames away from a previously scheduledframe, wherein the offset may be given by ceiling (L/d). The sameapplies to receptions to accommodate the reverse direction of the link.Correspondingly, the configured initial (network-wide) link load d maybe validated such thatd>=ceiling(L/m) where,

-   -   d is the number of like operations with a specific neighbor        needed within a cycle (i.e., there will be d transmissions to        the neighbor and d receptions from the neighbor). If d were        configured such that d<ceiling(L/m), then it should be        overwritten as d=ceiling(L/m) so as to ensure the link        maintenance cycle requirement is satisfied, specifically,        if d<ceiling(L/m) then d=ceiling(L/m).

The corresponding offset value as mentioned above is determined aso=ceiling(L/d) where,

-   -   o is the offset between like operations to a specific neighbor,        (i.e., like operations may be scheduled every o frames).

Furthermore, as a measure toward improving the latency of protocols,receptions may be scheduled such that they are evenly interleaved withthe transmissions, and thus the starting offset for searching for idleframes when scheduling receptions is given byRx_start_(—) o=ceiling(o/2), where

-   -   Rx_start_o is the approximate separation between a transmission        and a subsequent reception to the same neighbor.

This may allow a two-way handshake between two nodes to complete withinone maintenance cycle from the time of the first sent message, where ineffect, there are d such maintenance cycles of length o within a singlesteady-state communications (TDPA) schedule cycle. The starting offsetmay exceed whatever time is required to “turn a message around” in aprotocol, and thus by definition, the maintenance cycle length should,at a minimum, be twice that “turn around” time. By offsetting thereceptions, time for a two-way handshake to complete is reduced whichmay help latency of any multi-message protocol.

In an aspect of the invention, an “LE interrogator” may be defined asthe node which sends the first message in the handshake and the “LEresponder” as the node that receives and hears it. Because nodes maypotentially hear multiple other nodes during their scan, a node thatinitially hears the first message in the link establishment protocolattempt, sets up to complete that protocol attempt with that particularpeer before entering the handshake with any other (i.e., nodes ignoreany other LE interrogators while a handshake in the role of responder isin progress). Because in doing this, a single LE interrogator may havemultiple nodes responding to it, while at the same time the LEinterrogator may be itself a responder to a received LE interrogation,orderly coordination of bandwidth allocations may be achieved if the LEresponder initiates the IBA protocol. This may allow the LE Interrogatorto be the single point making the final bandwidth allocation.Specifically the LE responder is the IBA interrogator. In the IBAhandshake, a node may present its peer with the list of frames that arecurrently unreserved (idle) within its steady-state schedule. The peerlooks at its own steady-state schedule to identify frames that arecommonly idle and selects among those the requested number of frames forcommunicating in each direction of the link. This number represents theinitial bandwidth allocations.

Returning to FIG. 3, upon being powered “on,” each of node's (304-308)steady-state schedules begins as a pool of L idle frames (330). In theexample of FIG. 3, twenty frames have been selected as the fixed lengthschedule (302) but those skilled in the art will realize that L may be aconfigurable parameter and may be configured to any number of frames. Inaddition, an initial bandwidth allocation may be configured which maydetermine the number of opportunities a node may attempt to communicatewith other nodes during a cycle of the steady-state schedule. In thisexample, the initial bandwidth allocation may be set to two attempts perschedule cycle.

As shown in FIG. 3, during a discovery scan, nodes 1, 3, 9, and 11(304-308) search for peers using a randomized subtemplate approach inwhich communications operations (transmissions—Tx vs. receptions—Rx) arerandomized, while Tx bearings are a function of frame of day (Rx maytake place on the omni-directional mode as illustrated in FIG. 3). Inparticular, FIG. 3 shows nodes 1 (304) and 9 (308) transmitting a linkestablishment request, whereas nodes 3 (306) and 11 (310) are waiting toreceive a link establishment request.

As also shown in FIG. 3, transmission of data occurs when the transmitand receive arrows for the various nodes are pointed at or towards eachother representing that the highly directional antennas for both nodeshave been pointed in each other's direction. As illustrated in FIG. 3,the various nodes are transmitting with their respective directionalantennas in different directions at different times so as to makecontact with other peers.

FIG. 4 illustrates nodes prior to network formation and steady-stateschedule coordination in accordance with an aspect of the invention. InFIG. 4, nodes 1, 3, 9, and 11 (304-308) have yet to find any peers tocommunicate with but they continue to search via the randomizeddiscovery scan. However, nodes 9 (308) and 11 (310) are now transmittinga link establishment request, whereas nodes 1 (304) and 3 (306) arewaiting to receive a link establishment request.

FIG. 5 illustrates nodes 1, 3, 9, and 11 (304-308) participating in arandomized discovery scan in accordance with an aspect of the invention.As shown in FIG. 5 nodes 1, 3, 9, and 11 (304-308) may still be lookingfor peers to establish communications with via the randomized discoveryscan. In FIG. 5, nodes 1 (304) and 11 (310) are waiting and listeningfor a link establishment request, whereas nodes 3 (306) and 9 (308) aretransmitting a link establishment request. Furthermore, nodes 1, 3, 9,and 11 (304-308) as shown in FIGS. 4-5 are illustrated with theirrespective directional antennas transmitting in different directions atdifferent times so as to make contact with other peers. Those skilled inthe art will realize that the though the patterns in FIGS. 4-5 have beenshown sequential in a clockwise manner, antenna direction for each ofthe nodes may be randomized (non-sequential) in different embodiments.

FIG. 6 illustrates receipt of a transmission (602) from node 3 (306) tonode 1 (304) in accordance with an aspect of the invention. In FIG. 6,node 1 (304) hears the link establishment request from node 3 (306). Forthis instance of the handshake, node 3 (306) is the link establishmentinterrogator and node 1 (304) is the link establishment responder.

In FIG. 7, the link establishment responder node 1 (304) may also be theinitial bandwidth allocation interrogator. In an aspect of theinvention, node 1 (304) may offer all of its idle frames 0-19 (702) tolink establishment interrogator (IBA responder) node 3 (306) in theinitial bandwidth allocation request (IBA Req.). The idle frames in FIG.7 (702) may be represented by the question marks. In FIG. 7, twomessages 704 may be communicated between node 1 (304) and node 3 (306).The first message may be a link establishment response and the secondmessage may be an initial bandwidth allocation request.

In FIG. 8, the LE interrogator (IBA responder) node 3 (306) may select afew common idle frames between its schedule and node 1's schedule toallocate initial bandwidth over both directions of the link with node 1(304). The selection may be included in the IBA Rsp. For example, node 3(306) may select frames 0 and 10 for transmission to Node 1 (304)represented by X′ (802) and frames 5 and 15 for receiving informationrepresented by X (804) from node 1 (304). Moreover, node 3 (306) maystrive to stagger like operations in order to satisfy maintenance cyclerequirements. In an embodiment, the idle frames may be selected to levelthe transmission load and avoid jitter and/or latency problems.

In FIG. 9, upon successful completion of the LE and IBA handshakes, bothnodes may update their steady-state schedule accordingly. During timenot reserved for steady-state communications with neighbors, nodes maycontinue to search for peers. For example, node 1 (304) has reservedtime frame 0 and 10 (902 and 904) for receiving information from node 3(306). In addition, node 1 (304) has reserved time frame 5 and 15 (906and 908) for transmitting information to node 3 (306). Also, as shown inFIG. 9 node 3 (306) has reserved time frame 0 and 10 (910 and 912) fortransmitting information to node 1 (304) and time frames 5 and 15 (914and 916) for receiving information from node 1 (304). Furthermore, inFIG. 9 during the time not reserved for steady-state communications node11 (310) may be transmitting or listening for a link establishmentrequest.

The steady-state schedules of nodes 1 (304) and node 3 (306) have beenupdated. In FIG. 10, node 3 (306) hears the link establishment requesttransmitted (1002) from node 9 (308) in accordance with an aspect of theinvention. For this instance of the handshake, node 9 (308) may be a LEinterrogator and node 3 (306) a LE responder. During the handshakebetween nodes 9 (308) and 3 (306) communications may take place betweennodes 1 (304) and 3 (306) without any effect on the link establishmentand initial bandwidth allocation between nodes 9 and 3.

FIG. 11 illustrates that the LE responder node 3 (306) may also be theIBA interrogator. Node 3 (306) may offer all of its idle frames 1104 toits LE interrogator (IBA responder) node 9 (308) in the IBA Req. Theidle frames in FIG. 11 may be represented by the question marks. In FIG.11, two messages 1106 may be communicated between node 3 (306) and node9 (308) in accordance with an aspect of the invention. The first messagemay be a link establishment response and the second message may be aninitial bandwidth allocation request.

In FIG. 12, the LE interrogator (IBA responder) node 9 (308) may selecta few common idle frames between its schedule and node 3's schedule toallocate initial bandwidth over both directions of the link with node 3(306) and includes its selections in the IBA Rsp. For example, node 9(308) may select idle frames 1 and 11 for transmission to Node 3 (306)represented by X′ (1202) and frames 6 and 16 for receiving informationrepresented by X (1204) from Node 3 (306). Moreover, Node 9 (308) maystrive to stagger like operations in order to satisfy maintenance cyclerequirements. In an embodiment, idle frames may be selected to level thetransmission load and avoid jitter and/or latency problems.

Upon successful completion of the LE and IBA handshakes, both nodes mayupdate their steady-state schedule accordingly without having to notifyor affect any other node in the network as illustrated in FIG. 13.During time not reserved for steady-state communications with neighbors,nodes continue to search for peers. For example, nodes 1 (304) and 11(310) as shown in FIG. 13 may be transmitting a link establishmentrequest and nodes 3 (306) and 9 (308) may be listening for such requestsat a specific time frame such as time frame 2 (1302). Those skilled inthe art will realize that time frame 2 (1302) is merely exemplary andthat any time frame not reserved may be utilized.

Continuing the process of network formation and steady-state schedulecoordination, in FIG. 14 node 9 (308) hears the link establishmentrequest (1402) transmitted from node 11 (310). For this instance of thehandshake, node 11 (310) may be a LE interrogator and node 9 (308) is aLE responder. During the handshake (1402) between nodes 11 (310) and 9(308) communications may take place between nodes (1 and 3) and (3 and9) without any effect of the link establishment and initial bandwidthallocation between nodes 11 (310) and 9 (308).

FIG. 15 illustrates that the LE responder node 9 (308) may also be anIBA interrogator. Node 9 (308) may offer all of its idle frames to itsLE interrogator (IBA responder) node 11 (310) in an IBA Req. The idleframes (1502) in FIG. 15 may be represented by question marks. In FIG.15, two messages 1504 may be communicated between node 9 (308) and node11 (310). The first message may be a link establishment response and thesecond message may be an initial bandwidth allocation request.

In FIG. 16, the LE interrogator (IBA responder) node 11 (310) may selecta few common idle frames between its schedule and node 9's schedule toallocate initial bandwidth over both directions of the link with node 9(308) and includes its selections in the IBA Rsp. For example, node 11(310) may select idle frames 0 and 10 for transmission to node 9 (308)represented by X′ (1602) and frames 5 and 15 for receiving informationrepresented by X (1604) from Node 11 (310). Moreover, node 11 (310) maystrive to stagger like operations in order to satisfy maintenance cyclerequirements. In an embodiment, idle frames may be selected to leveltransmission load and avoid jitter and/or latency problems.

Upon successful completion of the LE and IBA handshakes, both nodes mayupdate their steady-state schedules (318 and 320) accordingly withouthaving to notify or affect any other node in the network as illustratedin FIG. 17. As illustrated in FIG. 18, during time not reserved forsteady-state communications with neighbors, nodes may continue to searchfor additional peers. For example, nodes 1 (304) and 9 (308) may betransmitting a link establishment request and nodes 3 (306) and 11 (310)may be listening for such a request at a specific time frame such asframe 4 (1802). Those skilled in the art will realize that time frame 4is merely exemplary and that any time frame not reserved may beutilized.

Continuing the process of network formation and steady-state schedulecoordination in FIG. 19, node 11 (310) hears the link establishmentrequest transmitted (1902) from node 3 (306). For this instance of thehandshake, node 3 (306) may be a LE interrogator and node 11 (310) is aLE responder. During the handshake between nodes 11 (310) and 9 (308)communications may take place between nodes (1 and 3), (3 and 9), and (9and 11) without any effect of the link establishment and initialbandwidth allocation between nodes 11 (310) and 3 (306).

FIG. 20 illustrates that the LE responder node 11 (310) may also be theIBA interrogator. Node 11 (310) may offer all of its idle frames to itsLE interrogator (IBA responder) node 3 (306) in the IBA Req. The idleframes (2002) in FIG. 20 may be represented by question marks. In FIG.20, two messages (2004) may be communicated between node 11 (310) andnode 3 (306). The first message may be a link establishment response andthe second message may be an initial bandwidth allocation request.

In FIG. 21, the LE interrogator (IBA responder) node 3 (306) may selecta few common idle frames (2102) between its schedule and node 11 (310)schedule to allocate initial bandwidth over both directions of the linkwith node 11 (310) and includes its selections in the IBA Rsp. Uponsuccessful completion of the LE and IBA handshakes, both nodes mayupdate their steady-state schedule accordingly without having to notifyor affect any other node in the network as illustrated in FIG. 22.During time not reserved for steady-state communications with neighbors,nodes may continue to search for new peers.

In another aspect of the invention, the protocols may be extended toinclude QoS to make a determination of a value of the nodes data todetermine which nodes receives the bandwidth.

Another example of link establishment and initial bandwidth allocationis shown below in FIGS. 23-32. Furthermore, in FIGS. 23-32, the processmay be shown using a sub-template based approach. In FIG. 23, a node maybe powered “on” and become operational. The node may participate in adiscovery scan. The direction of a node's transmission may berepresented in each frame using the notation b(f). For example, FIG. 23illustrates two nodes: a node i (2304) and a node j (2306) wherein innode i (2304) is powered “on” (2302). Initially node i (2304) mayschedule three subtemplates (2308) of s frames each, where s may be atleast the amount of time it takes for a node to turnaround a receivedmessage. The three subtemplates (2308) may be intended for use in eithertransmitting or receiving a first link establishment message (LE Req.).For illustrative purposes assume in FIG. 23 that node i (2304) is notaware of any other nodes on power up and node j (2306) is a node that isalready part of an existing network. Furthermore, the arrow (2360)indicates a time reference to be used throughout the exemplaryembodiment to depict time elapsing.

In accordance with an aspect of the invention, FIG. 24 shows that on allTx frames of the first subtemplate, node i (2304) sends a linkestablishment request (LE Req.). For example, at bearing b1 (2401) alink establishment request is transmitted as shown by 2402. Similarly,at bearing b3 (2403) a link establishment request is transmitted asshown by 2404. Finally, at bearing b4 (2405) a link establishmentrequest is transmitted as shown by 2406. As those skilled in the artwill realize, the direction in which each of the nodes points fortransmission purposes may be a function of the frame of day. Inaddition, the arrows (2402) and (2406) depicting transmission by node i(2304) do not get heard or detected by node j (2306) as indicated by thearrows (2402 and 2406) falling short of node j (2306).

In an aspect of the invention, node i's transmitted LE Req includes allunreserved (non-steady-state) Rx frames in the subsequent sub-templateas indicated by the asterisks 2410. In other words, node i (2304) maycommunicate to node j (2306) when it will be listening for a responsefrom node j (2306) (or any node that may have heard a link establishmentrequest during the present subtemplate) during the next subtemplate thatcorresponds to reception.

FIG. 25 illustrates that node j (2306) which is participating in anetwork hears node i's LE Req and randomly selects n frames (2502) ofthose offered in the LE Req in which to respond with an LE Rsp in thenext subtemplate. Node j (2306) may strive to avoid preemption of itsown steady-state communication and overwrites whatever operations it hadscheduled prior to receiving the LE Req. Only if all the frames offeredin the LE Req are currently being used for node j's steady-statecommunications with its neighbors, does node j (2306) preempt any framesfor responding to node i (2304).

In an aspect of the invention, n may be a function of the maximum numberof allowed neighbors and the number of Rx frames offered in node i's LEReq, where its minimum value may be 1. In the example, n=2 as depictedby the two frames that node j selects in which to transmit its response.Similarly, node j (2306) may also select one of its non-steady-stateframes during the third subtemplate in which it is to point in node i'sdirection for receiving the third and last message in the linkestablishment handshake (as well as the piggy-backed last message in theinitial bandwidth allocation handshake), an LE Ack/IBA Rsp. Node j(2306) may also look at its steady-state schedule so that it may conveyto node i (2304) all of its idle frames within the steady-statecommunications schedule in the IBA Req.

FIG. 26 illustrates that upon completion of a subtemplate t (we reach asubtemplate boundary) nodes randomly schedule any frames not reservedfor steady-state communications (i.e., any idle frames) of subsequentsubtemplate t+3. This gives nodes 3 s frames worth of look-ahead time.In an alternative embodiment, nodes may initially schedule 2 s-framesubtemplates and on every frame, schedule a new frame if not reservedfor steady-state communications. For example, FIG. 26 shows a newsubtemplate (2602) such that three subtemplates are prescheduled inadvance.

FIG. 27 illustrates that node j (2306) attempts to respond (with the LERsp/IBA Req 2702) on multiple opportunities on the frames that node j(2306) may have previously selected for responding to node i (2304).This message conveys both the time in the subsequent subtemplate whennode j (2306) is to be listening in node i's direction for its LEAck/IBA Rsp 2702, and the list of node j's idle frames within itssteady-state schedule. As those skilled in the art will realize, in thisexemplary embodiment this is the first time node i (2304) hears aboutnode j (2306).

In an aspect of the invention, node i (2304) hears node j's LE Rsp/IBAReq (2702). Node i (2304) may ignore any subsequent responses andpossibly LE requests from node j (2306) except maybe to update itsknowledge of node j's position and thus its pointing angle toward node i(2304).

FIG. 28 illustrates that node i (2304) may now be aware (2802) of whennode j (2306) may be listening in its direction because of nodes j'stransmission. Node i (2304) may look at its steady-state schedule andselect 2*d frames that are commonly idle with those offered in the IBAReq, where d is the configured link load representing the initialbandwidth allocation which should correspond to at least the linkmaintenance rate. In an embodiment, d of those frames may be used fornode i (2304) to transmit to node j (2306) and the other d may be fornode j (2306) to transmit to node i (2304). Thus, the steady-statecommunications schedule between nodes i (2304) and node j (2306) isbeing coordinated (d frames are reserved for each direction of thelink).

In addition, node i (2304) may reserve the opportunity within thesubtemplate to transmit the LE Ack/IBA Rsp. In one aspect of theinvention, if node i (2304) were also participating in a network, node i(2304) may have to preempt a steady-state communication frame, but onlyfor this subtemplate.

FIG. 29 illustrates that once again upon completion of a subtemplate,nodes randomly schedule any frames not reserved for steady-statecommunications (i.e., any idle frames) of subsequent subtemplate t+3.This gives nodes 3 s frames worth of look-ahead time. For example, FIG.29 shows a new subtemplate (2902) such that three subtemplates areprescheduled in advance.

FIG. 30 illustrates that at the expected frame (3002), node i (2304)transmits a LE ACK/IBA Rsp (3004). The link may be consideredestablished from node i's point of view and its schedule with node j(2306) may also be established at node i (2304). Node i (2304) maytransition to use its steady-state communication opportunities with nodej (2306) within the next subtemplate time interval.

As shown in FIG. 31, upon reception of node i's LE Ack/IBA Rsp 3004, thelink is considered established from node j's point of view and itsschedule with node i (2304) is also established at node j (2303).Regardless of any previously reserved communication opportunities withother peers, node j (2306) may participate in the handshake, establishthe link, and coordinate bandwidth allocations with its newly acquiredneighbor without disturbing or impacting the rest of the network

Finally, FIG. 32 illustrates that upon completion of a subtemplate t attime reference (2360), nodes may randomly schedule any frames notreserved for steady-state communications (i.e., any idle frames) ofsubsequent subtemplate t+3 (not shown). For example, frame (3202) may beutilized as it is not reserved for steady-state communications. In anembodiment, all prior and those recently reserved frames for steadystate communications are in place independent of the link establishmentsubtemplate patterns. Moreover, both nodes may participate in additionalhandshakes with other discovered peers.

In another aspect of the invention, a sectorized directional antenna maybe used to increase reception range of a node. In an embodiment, asector of the directional antenna may be activated for reception. Thecoverage of the signal may be approximately 90 degrees.

The following description along with FIGS. 33-53 describes an aspect ofthe invention using a sectorized directional antenna during networkformation. The networking software implementation may be such thateither omni-based or directional sector-based link establishment may beenabled via a configurable parameter in the site configuration databaseas well as through manual command at run-time.

In an aspect of the invention using sectorized directional reception,allocation of some of the reception frames may be necessary. Thereception frames may be allocated specifically for receiving LinkEstablishment Requests (LE Req) and for receiving Link EstablishmentResponses (LE Rsp).

The receptions of a link establishment request may be in the oppositedirection (reciprocal bearing) in which link establishment requests aresent within the same subtemplate, while the reception of a linkestablishment response may be as close to the same direction in which alink establishment request was sent in the previous subtemplate.Specifically,if the B _(LE Req Tx) =f(FOD), it follows thatB _(LE Req Rx)=reciprocal of f(FOD) which we'll denote as ˜f(FOD), andthusB _(LE Rsp Rx) =B _(LE Req Tx (in the previous subtemplate)) =f(FOD−s),where,

-   -   B_(LE Req Tx) is the bearing at which a Link Establishment        Request is transmitted and is a function of frame of day when        the transmission is to take place, or f(FOD),    -   B_(LE Req Rx) is the bearing at which a Link Establishment        Request is to be listened for,    -   B_(LE Rsp Rx) is the bearing at which a Link Establishment        Response is to be listened for, and s is the subtemplate length        in unit of frames.

Because for Link Establishment requests heard during one subtemplatenodes respond during the subsequent subtemplate, the frame of day to usein determining the angle in which to point for receiving responsescorresponds to that used to send requests in the previous subtemplate.Upon receiving a Link Establishment request, a responder node may knowexactly where to point to transmit the response as it has knowledge ofits own and the interrogator's position. The same applies for thedirection in which the acknowledgement is to be sent as now theinterrogator may also know the position of the responder. The initialbandwidth allocation protocol is “piggy-backed” onto the linkestablishment handshake.

FIG. 33 illustrates nodes prior to network formation and steady-stateschedule coordination in accordance with an aspect of the invention. InFIG. 33, a scheduled cycle (3302) is depicted for node 1 (3304), node 3(3306), node 9 (3308), and node 11 (3310). The schedule cycle (3302) forthe illustrated nodes begins with a pool (an array) of L idle frames(3330), where L is a configurable parameter. L may be based on empiricaldata, perhaps even starting with a schedule that is in the order of thelegacy network's maximum schedule length. In an embodiment, L may be thelength of one steady-state schedule cycle. As a link is establishedbetween two nodes, the nodes coordinate the frames within that arrayduring which each node may transmit to the peer thus quickly and easilyallocating the initial bandwidth between them. The initial bandwidthallocation (IBA) handshake may be conducted such that communicationsover each direction of the link are agreed upon without risk ofconflicting reservations between a node and its multiple neighbors.

In FIG. 33, upon being powered “on,” each of node's (3304-3310)steady-state schedules begins as a pool of L idle frames (3330). In theexample of FIG. 33, twenty frames have been selected as the fixed lengthschedule (3302). In addition, an initial bandwidth allocation may beconfigured which may determine the number of opportunities a node mayattempt to communicate with other nodes during a cycle of thesteady-state schedule. In this example, the initial bandwidth allocationmay be set to two attempts per schedule cycle.

As shown in FIG. 33, during a discovery scan nodes 1, 3, 9, and 11(3304-3310) search for peers using a randomized subtemplate approach inwhich communications operations (transmissions—Tx vs. receptions—Rx) arerandomized, while Tx bearings are a function of frame of day. For Rxoperations, expected messages may also be selected randomly. The Rxbearings for the LE Req Rx may be the reciprocal to that of the LE ReqTx, and the Rx bearings for the LE Rsp Rx may be as close as possible tothe bearings used when the LE Req was heard. Directional Rx may be donewhen the node is aware of the peer's position. In particular, FIG. 33shows nodes 1 (3304) and 11 (3310) transmitting a link establishmentrequest, whereas nodes 3 (3306) and 9 (3308) are waiting to receive alink establishment request.

FIG. 34 illustrates nodes prior to network formation and steady-stateschedule coordination in accordance with an aspect of the invention. InFIG. 34, nodes 1, 3, 9, and 11 (3304-3310) continue to search forpotential new neighbors while powered “on.” The nodes may continue tosearch until powered “off”

FIG. 35 illustrates nodes 1, 3, 9, and 11 (3304-3310) participating in arandomized discovery scan in accordance with an aspect of the invention.As shown in FIG. 35 nodes 1, 3, 9, and 11 (3304-3310) may still belooking for peers to establish communications with via the randomizeddiscovery scan. In FIG. 35, nodes 1 (3304) and 3 (3306) are waiting andlistening for a link establishment request, whereas nodes 11 (3310) and9 (3308) are transmitting a link establishment request.

FIG. 36 further illustrates nodes prior to network formation andsteady-state schedule coordination in accordance with an aspect of theinvention. In FIG. 36, nodes 1, 3, 9, and 11 (3304-3310) continue tosearch for potential new neighbors via a randomized discovery scan whilepowered “on.” In FIG. 36, nodes 1 (3304) and 11 (3310) are waiting andlistening for a link establishment request, whereas nodes 3 (3306) and 9(3308) are transmitting a link establishment request.

FIG. 37 illustrates receipt of a transmission (3702) from node 3 (3306)to node 1 (3304) in accordance with an aspect of the invention. In FIG.37, node 1 (3304) is in range to hear the link establishment requestfrom node 3 (3306). The nodes may now transition to complete the linkestablishment protocol by coordinating time for completion of theexchange. In LE Req, node 3 (3306) may identify LE Rsp Rx frames infuture subtemplate.

In FIG. 38, node 1 (3304) selects available response frames among thoseoffered some time in the near future. Node 1 (3304) responds with an LEresponse. In addition, node 1 (3304) may also initiate an initialbandwidth allocation (IBA) protocol with an IBA Req. In an aspect of theinvention, node 1 (3304) may offer all of its idle frames 0-19 (3802) tonode 3 (3306). The idle frames in FIG. 38 (3802) may be represented byquestion marks. During the exchange, nodes may exchange positioninformation that may allow them to more precisely point at each other.The remaining nodes may continue to search for potential neighbors.

In FIG. 39, node 3 (3306) sends its LE Ack along with its IBA Rsp tocomplete both protocols. The IBA Rsp may select a few common idle framesbetween its schedule and node 1's schedule to allocate initial bandwidthover both directions of the link with node 1 (3304). For example, node 3(3306) may select frames 0 and 10 for transmission to Node 1 (3304)represented by X′ (3902) and frames 5 and 15 for receiving informationrepresented by X (3904) from node 1 (3304). Moreover, node 3 (3306) maystrive to stagger like operations in order to satisfy maintenance cyclerequirements. In an embodiment, the idle frames may be selected to levelthe transmission load and avoid jitter and/or latency problems.

In FIG. 40, nodes 1 and 3 (3304-3306) have coordinated the steady statecommunication opportunities between them and have formed a network. Thelink may be maintained on a TDPA schedule. During time not reserved forsteady-state communications with neighbors, nodes may continue to searchfor peers. For example, node 1 (3304) has reserved time frame 0 and 10(4002 and 4004) for receiving information from node 3 (3306). Inaddition, node 1 (3304) has reserved time frame 5 and 15 (4006 and 4008)for transmitting information to node 3 (3306). Also, as shown in FIG. 40node 3 (3306) has reserved time frame 0 and 10 (4010 and 4012) fortransmitting information to node 1 (3304) and time frames 5 and 15 (4014and 4016) for receiving information from node 1 (3304).

In FIG. 41, node 3 (3306) discovers (4102) node 9 (3308) in accordancewith an aspect of the invention. Node 3 (3306) and node 9 (3308) are inrange of each other and node 3 (3306) hears node 9's LE Req. Both nodesmay now transition to complete the link establishment protocol bycoordinating time for completion of the exchange. In the LE Req, node 9(3308) may identify LE Rsp Rx frames in the next subtemplate.

FIG. 42 illustrates that node 3 (3306) selects response frames amongthose offered. Node 3 (3306) responds with an LE Rsp and may alsoinitiate the initial bandwidth allocation (IBA) protocol with an IBAReq. Node 3 (3306) may offer all of its idle steady state frames 4204 tonode 9 (3308) in the IBA Req. During the exchange, nodes may haveexchanged position information that may allow them to more preciselypoint at each other. In addition, other nodes such as nodes 1 (3304) and11 (3310) may continue searching for potential neighbors.

In FIG. 43, node 9 (3308) may send its Le Ack along with its IBA Rsp tocomplete both protocols. The IBA Rsp may identify a few common idleframes between its schedule and node 3's schedule to communicate overboth directions of the link with node 3 (3306). For example, node 9(3308) may select idle frames 1 and 11 for transmission to Node 3 (3306)represented by X′ (4302) and frames 6 and 16 for receiving informationrepresented by X (4304) from Node 3 (3306). Moreover, Node 9 (3308) maystrive to stagger like operations in order to satisfy maintenance cyclerequirements.

Both nodes 3 (3306) and 9 (3308) have successfully coordinated theirsteady state communications opportunities between them and have becomeneighbors. The link 4402 may be maintained via steady statecommunications on a TDPA schedule as illustrated in FIG. 44. During timenot reserved for steady-state communications with neighbors, nodescontinue to search for peers. The process of network formation andsteady-state schedule coordination may continue in a similar manner fornodes 9 and 11 and nodes 11 and 3. As illustrated above using asectorized reception capability of a directional antenna, as link loadsare monitored during steady state communications, bandwidth allocationsmay be updated independent of link establishments.

FIGS. 45-53 illustrate the use of sectorized directional reception andthe scheduling of the discovery scan in accordance with an aspect of theinvention. In FIG. 45, a node may be powered “on” and becomeoperational. The node may participate in a discovery scan. For example,FIG. 45 illustrates two nodes: a node i (4504) and a node j (4506)wherein in node i (4504) is powered “on” (4508). Initially node i (4504)may schedule three random s-frame subtemplates (4510) of s frames each,where s may be at least the amount of time it takes for a node toturnaround a received message. The three subtemplates (4510) may beintended for use in either transmitting or receiving a linkestablishment request (LE Req) or a link establishment response (LERsp). The LE Rsp may also be piggybacked with an initial bandwidthallocation request (IBA Req). For illustrative purposes assume in FIG.45 that node i (4504) is not aware of any other nodes on power up andnode j (4506) is a node that is already part of an existing network.Furthermore, the arrow (4560) indicates a time reference to be usedthroughout the exemplary embodiment to depict time elapsing.

In accordance with an aspect of the invention, FIG. 46 shows that on allTx frames of the first subtemplate 4602, node i (4504) sends a linkestablishment request (LE Req) in the direction given by FOD. Node i'stransmitted LE Req identifies all LE Rsp Rx frames in the subsequentsub-template as indicated by the asterisks 4604. Bearings assigned to LEReq Rx frames are reciprocal to those being assigned to LE Req Txframes, hence on frame x of a subtemplate, b_(x) denotes the bearing theLE Req transmitter would use while ˜b_(x) denotes the bearing to use forLE Req Rx frames where ˜b_(x)=b_(x)+180 normalized to [0,360]. Bearingsassigned to LE Rsp/IBA Req Rx frames are in the same direction that theLE Reqs were transmitted in the previous subtemplate, hence on frame xof subtemplate y, b_(x-s) is used, where b_(x) is the bearing an LE Reqtransmitter would use at frame x of subtemplate y and s is the length ofa subtemplate in frames

FIG. 47 illustrates that node j (4506) which is participating in anetwork hears node i's LE Req and randomly selects n frames (4702) ofthose offered in the LE Req in which to respond with an LE Rsp in thenext subtemplate. Node j (4506) may strive to avoid preemption of itsown steady-state communication and overwrites whatever operations it hadscheduled prior to receiving the LE Req. If all the frames offered inthe LE Req are currently being used for node j's steady-statecommunications with its neighbors, then node j (4506) may preempt anyframes for responding to node i (450404).

In an aspect of the invention, n may be a function of the maximum numberof allowed neighbors and the number of Rx frames offered in node i's LEReq, where its minimum value may be 1. In the example, n=2 as depictedby the two frames that node j selects in which to transmit its response.Similarly, node j (4506) may also select one of its non-steady-stateframes during the third subtemplate in which it is to point in node i'sdirection for receiving the third and last message in the linkestablishment handshake (as well as the piggy-backed last message in theinitial bandwidth allocation handshake), an LE Ack/IBA Rsp. Node j(4506) may also look at its steady-state schedule so that it may conveyto node i (4504) all of its idle frames within the steady-statecommunications schedule in the IBA Req.

FIG. 48 illustrates that upon completion of a subtemplate t (reaching asubtemplate boundary) nodes randomly schedule any frames not reservedfor steady-state communications (i.e., any idle frames) of subsequentsubtemplate t+3. This gives nodes 3 s frames worth of look-ahead time.In an alternative embodiment, nodes may initially schedule 2 s-framesubtemplates and on every frame, schedule a new frame if not reservedfor steady-state communications. For example, FIG. 48 shows a newsubtemplate (4802) such that three subtemplates are prescheduled inadvance.

FIG. 49 illustrates that node j (4506) attempts to respond (with the LERsp/IBA Req 4902) on multiple opportunities on the frames that node j(4506) may have previously selected for responding to node i (4504).Node j (4506) may directly point toward node i (4504). To listen forresponses, node i (4504) points in a direction that is close to that inwhich the LE Req that was heard by node j (4506) was sent. The LE Rspconveys both the time in the subsequent subtemplate when node j (4506)is to be listening in node i's direction for its LE Ack/IBA Rsp, and thelist of node j's idle frames within its steady-state schedule.

In an aspect of the invention, node i (4504) hears node j's LE Rsp/IBAReq (4902). Node i (4504) may ignore any subsequent responses andpossibly LE requests from node j (4506) except maybe to update itsknowledge of node j's position and thus its pointing angle toward node i(4504).

FIG. 50 illustrates that node i (4504) may now be aware of when node j(4506) may be listening in its direction and may point directly at nodej (4506). Node i (4504) may look at its steady-state schedule and select2*d frames that are commonly idle with those offered in the IBA Req,where d is the configured link load representing the initial bandwidthallocation which should correspond to at least the link maintenancerate. In an embodiment, d of those frames may be used for node i (4504)to transmit to node j (4506) and the other d may be for node j (4506) totransmit to node i (4504). Thus, the steady-state communicationsschedule between nodes i (4504) and node j (4506) is being coordinated(d frames are reserved for each direction of the link).

In addition, node i (4504) may reserve the opportunity within thesubtemplate to transmit the LE Ack/IBA Rsp. In one aspect of theinvention, if node i (4504) were also participating in a network, node i(4504) may have to preempt a steady-state communication frame, but onlyfor this subtemplate.

FIG. 51 illustrates that once again upon completion of a subtemplate,nodes randomly schedule any frames not reserved for steady-statecommunications (i.e., any idle frames) of subsequent subtemplate t+3.This gives nodes 3 s frames worth of look-ahead time. For example, FIG.51 shows a new subtemplate (5102) such that three subtemplates areprescheduled in advance.

FIG. 52 illustrates that at the expected frame (5202), node i (4504)transmits a LE ACK/IBA Rsp (5204). The link may be consideredestablished from node i's point of view and its schedule with node j(4506) may also be established at node i (4504). Node i (4504) maytransition to use its steady-state communication opportunities with nodej (4506) within the next subtemplate time interval.

As shown in FIG. 53, upon reception of node i's LE Ack/IBA Rsp, the linkis considered established from node j's point of view and its schedulewith node i (4504) is also established at node j (4506). Regardless ofany previously reserved communication opportunities with other peers,node j (4506) may participate in the handshake, establish the link, andcoordinate bandwidth allocations with its newly acquired neighborwithout disturbing or impacting the rest of the network.

Adaptive Component of Medium Access Control

In the event that during link establishment and initial bandwidthallocation, no set of common idle frames are found such that the evenstaggering of communications for satisfaction of the maintenanceschedule cycle can be accommodated, the entire handshake may beconsidered unsuccessful. In this event, a mechanism may be put in placesuch that nodes may re-allocate bandwidth to other peers in order to“free” other frames within the cycle that will allow the previous linkestablishment attempt to succeed in a future attempt. Specifically, anode knowing the idle frames of a peer with which it recently attemptedto establish a link, looks at its own schedule to determine which peers'allocation may be shifted.

Utilization of bandwidth may be averaged through the use of a link loadmonitoring cycle to prevent oscillation between allocations for varyinginstant traffic loads. Upon detecting the need to change the bandwidthallocated to a neighbor, a node may initiate a protocol with theneighbor so that the two nodes may coordinate changes to their localschedules. This may entail the addition or deletion of communicationopportunities. Upon successful completion of the protocol, two nodes mayimmediately begin using their updated local schedules and thus in theevent of increased bandwidth from a node to a neighbor, achieve promptrelief in that the amount of data previously sitting in the queuewaiting to be sent to the neighbor may be sent, and any data that wouldfollow would not need to be discarded because the new allocations wouldsuffice. If instead, bandwidth allocations need to be decreased, theresulting deletion of communication opportunities would provide the twonodes involved additional idle frames to possibly use later forincreasing the bandwidth allocation to another neighbor if needed.

Whenever the desired allocations may be accommodated within the currentschedule, the resulting changes only affect the two nodes involved andhave no effect on the schedules being followed by any other nodes in thenetwork and may for this reason, be applied quickly without requiringnetwork-wide coordination.

To determine whether or not the current bandwidth allocation issufficient or excessive for the amount of data waiting to be sent toeach neighbor, each node may periodically monitor the ingress data rate,i.e., the number of bytes being placed in the outbound queuecorresponding to each neighbor over the length of the monitoring period.Specifically, as a node sources or receives a frame of data to beforwarded, it places it in the Data Link Layer's outbound queuecorresponding to the neighbor that represents the next hop in the pathtoward the data's destination. To do this, an ingress byte counter foreach neighbor's queue may be reset at the beginning of each loadmonitoring cycle and subsequently incremented by the size of the databeing placed in the queue during its duration. As a frame is thentransmitted (i.e., the data is removed from the queue for delivery),another counter may be kept to track the egress data rate which would beincremented by the size of the data being sent out.

For a node to determine the actual bandwidth allocated to each neighborit may be aware of the following: the number of transmissions to thatneighbor within a steady-state schedule cycle (or current load), thesteady-state schedule cycle length, the data rate being sustained overthat direction of the link, the duration of a frame, and the length ofthe monitoring period. To facilitate the computation of the ingress datarate and of bandwidth allocation, the length of the load monitoringcycle k may be a multiple of the schedule cycle length, where k>=2 whend=1, but k>=1 otherwise. This may allow for the bandwidth allocationupdate protocol that may be initiated at the end of a monitoring cycleto complete, which could take up to approximately 1.5 maintenanceschedule cycles, before possibly triggering another instance of theprotocol. By making this value a configurable resource, it may befine-tuned to enhance network performance. Furthermore, while theprotocol is conducted, monitoring should be disabled, because the“relief” being provided via the bandwidth allocation update protocol isnot yet in place until the protocol completes.

From knowledge of the local schedule, each node may be aware of thenumber of transmissions to each neighbor i currently within a cycle orcurrent load, (cTx_cnti). This value may in fact be initialized to theconfigured initial link load. Given the data rate currently beingsustained over the link to each neighbor and the duration of a frame,the node may also calculate the current capacity of the link as theamount of data that may be sent in one frame (in one transmission) toeach neighbor i. In other words, the link's data rate may be expressedin units of bytes per frame asdoi=dr*f/8

-   -   where,    -   doi is the amount of data sent in one frame (in bytes per        frame),    -   dr is the link data rate (in bits per second), and    -   f is the frame duration (in seconds per frame)

At the end of the load monitoring cycle, the ingress byte countermentioned above, (iByte_cnti), reflects the number of bytes depositedinto the queue for neighbor i for the duration of one monitoring cycle,compensated for the overhead that is to be added in the form ofheader/control information. This measure of overhead may be determinedfrom previous monitoring periods and provides merely an estimate, as theactual size of the overhead is not known until the data is actuallypackaged.

Specifically,iByte_(—) cnti=NL_Byte_(—) cnti+overhead

-   -   where,    -   NL_Byte_cnti is the byte count being deposited in the queue for        neighbor i, and overhead is the estimated amount (perhaps a        running average) of header/control data to be added once the        data is packaged to go out,

To obtain the number of transmissions within a schedule cycle necessaryto support that ingress data rate, a node uses the value in thiscounter, the data rate over the link, and the number of schedule cycles(k) within a monitoring cycle. The difference between what results andthe number of transmissions currently in place within the schedule mayyield the number of transmissions that if added, would have allowed forany data left in the queues to be sent. Namely,dTx _(—) cnti=ceiling[(iByte_(—) cnti/(doi*k)]−cTx _(—) cnti

-   -   where,    -   dTx_cnti is the number of transmissions to neighbor i to be        “added” into the schedule cycle in order to meet its bandwidth        demands (in frames),    -   iByte_cnti is the amount of data deposited into the queue for        neighbor i during the monitoring cycle (in bytes),    -   doi is the amount of data that can be sent over the link in one        frame (in bytes), and k is as defined above.

It may be evident to those skilled in the art that the differencedTx_cnti may reflect a negative value, indicating that bandwidth isbeing underutilized, and thus the allocation to that particular neighbormay be reduced by removing transmissions from the schedule. A differenceof 0 may reflect that the bandwidth allocation to a neighbor is justright and that the amount of data being placed in the queue should besuccessfully sent over the link. A positive value may indicate that thecurrent bandwidth allocation is insufficient for the amount of datawaiting to be sent out. In general, each observed difference value mayreflect the number of transmissions to a neighbor that may beadded/deleted to/from the two nodes' current local schedules. This doesnot present any problems in the event that transmissions are to bedeleted, because that change may be readily accommodated at both nodesby making previously reserved communications into idle frames. However,for the case in which transmissions are to be added, there exists anissue of finding a sufficient number of common idle frames with theneighbor in order to change them into communication operations asexplained below.

Whenever the observed value of dTx_cnti is non-zero, all the aboveparameters may be recorded for post-testing analysis and debuggingpurposes. The determination of the difference dTx_cnti can be made basedon a fixed schedule length. In the event that the schedule is denselypopulated, or that the need to increase the allocation of bandwidthapplies to numerous neighbors, it may eventually be increasinglydifficult for the nodes involved to find enough common idle framesbetween them to accommodate all the desired updates, and thus a largerschedule may be required (i.e. schedule length would necessarilyincrease).

The use of the ceiling function in the equation in effect “rounds up” tothe nearest whole transmission resulting in bandwidth allocationrequests that indicate the need for the exact bandwidth or more than isactually needed.

Lastly, in the event that the desired relief can only be partiallyaccommodated (i.e., only partial success of the update is possible), theapproach will be to implement as much of it as possible. Specifically,if dTx_cnti holds a positive number, but fewer (1 or more but not quitedTx_cnti) can be accommodated, the node should initiate the protocol tocoordinate the addition of as many temporary transmissions as can beadded. The objective is to provide as much relief as quickly aspossible. When only partial relief is accommodated and the situationrequiring persists, a subsequent attempt would take place to try toincrease the portion of the bandwidth allocation that was notaccommodated. That instance of the protocol should then result in atotal failure. A node could then use this information to preventconstantly trying to add bandwidth when none is available. To do this, anode should not attempt the protocol with a neighbor with which aprevious attempt resulted in complete failure, until the node hasdecreased its allocations to any of its neighbors, thus freeing upbandwidth that could now possibly be allocated to the neighbor withwhich a previous attempt failed.

For healthy (i.e., physically sustainable) links for which bandwidth isunderutilized (the difference dTx_cnti reflects a negative value), thebandwidth allocations are not allowed to drop below the initiallyconfigured value of d transmissions in a schedule cycle so as tocontinue to maintain the link (keep the link “alive”) according to oneembodiment. In another embodiment, only if a link was deemed physicallyunsustainable and this was consequently reflected as a connectivitychange (lost link), would the current number of frames reserved forcommunication opportunities to the neighbor with which the link waslost, be returned to the pool of idle frames.

Upon partial or total success of the protocol, the two nodes involvedupdate their local schedules to the extent possible, providing quickrelief toward satisfying the bandwidth demands of the neighbor. Thenodes can begin using any newly added communication opportunitiesimmediately or dispose of newly made idle frames for increasingbandwidth allocations to other neighbors.

Even though the bandwidth allocations are evaluated for all neighborsduring each monitoring cycle, one thing to consider is whether the nodeshould respond to all its neighbors' situations simultaneously, or ifinstead, a single neighbor's situation should be handled during eachcycle. Doing the former would cause the node to possibly attemptnumerous instances of the bandwidth allocation update protocol with itsneighbors. However, assuming the desired updates include only a few orno bandwidth allocation decreases the likelihood of being able toaccommodate allocation increases to multiple neighbors, goes down as thenumber of neighbors requiring adjustment goes up since the number ofidle frames in a node's schedule would be quickly consumed. A node inthis situation might not even be able to complete the various protocolinstances. If instead, the response for each monitoring cycle is appliedto a single neighbor, the amount of possible network management trafficcould be reduced at the cost of possibly delaying temporary reliefrequired by other neighbors. However, if the relief needed by a nodethat is not being responded to is of a permanent nature, then it wouldfollow that the demand would remain and eventually be accommodated asthe particular neighbor's turn comes up. The approach could be torespond to each neighbor in turn (i.e., in round-robin order) forfairness, or alternatively, to respond to the neighbor that most needsrelief (i.e., that for which the observed difference value is thehighest, since this would be the neighbor in “worst shape”). Initially,the approach will be the latter, since it is expected that once itssituation is addressed, a different neighbor's situation would becomethe one with most urgency.

An aspect of the invention provides for a bandwidth allocation updateprotocol. This protocol may be similar to the Initial BandwidthAllocation protocol. Similar to the IBA handshake, it is defined as atwo-way handshake between an initiating node and one of its neighbors.Rather than holding off monitoring while retrying additional attempts ofthe protocol when it fails (times out), a single attempt will betriggered at the end of a monitoring period (when dTx_cnti is not 0). Ifthe protocol times out, and the situation that required the update inthe first place persists, the subsequent monitoring period may result intriggering the protocol once again, with the added advantage that theupdate request will reflect a more current situation. If the protocolfails but the situation was merely temporary, the next monitoring periodshould have a different outcome. If the protocol succeeds and fixes apersistent situation, then the following monitoring period may result inthe protocol not being triggered (dTx_cnti is 0). The timeout value touse for a single attempt may be estimated from knowledge of theresulting maintenance cycle length o, since at the very least, therewill be communication opportunities within a single maintenance cycle tocomplete a two-way handshake. However, if the initiator node'stransmission opportunity to the neighbor was just missed, the handshakemay have to be attempted in the next maintenance schedule cycle. Forthis reason, the timeout for each attempt of the protocol may be set to2*o.

In general, as a node assesses the demands of all its neighbors, at theend of each monitoring cycle, the node may select the neighbor needingthe most substantial update for which, from knowledge of its own localschedule and the type of desired update, success of accommodating it isprobable (i.e., the node has idle frames in its local schedule).Specifically, the success of an update in which communicationopportunities are to be deleted is always highly probable. The partialor total success of an update in which communication opportunities areto be added however, is only probable if the initiating node has atleast one idle frame in its local schedule. If a node has at least oneidle frame that may be used to accommodate at least a partial, andhopefully total update, and without having up-to-date knowledge of theneighbor's local schedule and its set of currently idle frames, the nodemay attempt the protocol.

The exchange is successful if the two nodes can coordinate a completeupdate to their local schedules. When the exchange is used for thepurpose of decreasing bandwidth allocation, it follows that the exchangeshould succeed as long as the link is healthy (i.e., environmentalconditions support the currently assessed capacity of the link and themessages can get through to the nodes). However, the node may not wantto initiate the protocol when the observed value of dTx_cnti isnegative, if cTx_cnti=d. This ensures that even if underutilized,sufficient bandwidth remains allocated to at least maintain the link viathe configured d transmissions within the cycle.

The first message in the handshake may be the Bandwidth AllocationUpdate Request (BAU Req), with which the initiating node informs theneighbor about the type of update and the desired amount of the update(i.e., addition or deletion of communications and how many). This maycome from the value of the observed difference dTx_cnti where, apositive value denotes the addition of transmissions, and a negativevalue denotes the deletion of transmissions. In the case of addingbandwidth, the initiating node may also provide to the neighbor,information on where this update could be incorporated into the twonodes' local schedules via its list of idle frames.

Each time a node participates in an instance of the bandwidth allocationupdate protocol, the nodes involved, their role (initiator vs.responder), the type and amount of desired update, the nodes' schedulesbefore and after the update, the selected frames to be changed, and theoutcome (failure, partial success, or success) if possible, should berecorded at the node possessing such knowledge (which could be bothnodes) for post-testing analysis and debugging purposes.

An exemplary embodiment of the adaptive bandwidth allocation isillustrated below in FIGS. 54-60. In FIG. 54, a node 3 (5406) detectsthat perhaps due to a drop in data rate over its link (5405) to node 9(5408), more data is being queued to go to node 9 (5408) than before.Node 3 (5406) may initiate a bandwidth allocation update (BAU) protocolin which it coordinates the addition of a number of transmissions tonode 9 (5408) (1 in this example). Similar to IBA, node 3 (5406) mayoffer its idle frames to node 9 (5408) in a BAU Req.

As illustrated in FIG. 55, a BAU handshake may take place on the alreadyreserved communication opportunities within the steady state schedulebetween the two nodes. Node 9 (5408) may select an idle frame (5502) incommon with node 3 and include its selection in the BAU Rsp.

Upon completion of the handshake, both nodes 3 (5406) and 9 (5408)update their steady state schedules 5413 (at 5604) and 5418 (at 5602) asshown in FIG. 56. With added bandwidth, node 3 (5406) should be able totransmit the traffic being queued up for which node 9 (5408) is the nexthop toward the destination.

As illustrated in FIG. 57, during time not reserved for steady statecommunications with neighbors, nodes 1 (5404), 3 (5406), 9 (5408) and 11(5410) continue to search for peers. Added bandwidth between nodes 3(5406) and 9 (5408) stays in effect while the condition that provoked itpersists. BAU may be used to also decrease bandwidth allocations

In FIG. 58, a link between nodes 3 (5406) and 9 (5408) has becomeunsustainable. Link management function drops the link and the two nodesdelete all communication operations between them. Note that thesituation may apply to a single direction of a link. In this examplehowever, both directions of the link are shown as being unsustainabledue to both nodes moving beyond each others range.

In FIG. 59, a link between nodes 3 (5406) and 11 (5410) also becameunsustainable. However, not enough data was being sent over that link atthe time and for this reason, bandwidth updates were not triggeredbetween them and the link was subsequently dropped.

In FIG. 60, nodes may move beyond communications range or are no longerin line of sight. For example in FIG. 60, with links (3, 9) and (3, 11)now none existent, the original network has split into two networks thefirst network between nodes 1 and 3 (6002) and the second between nodes9 and 11 (6004). Schedules of all nodes are adapted without impactingthose of any other node in the previous or the two resulting networks

In another aspect of the invention, an exemplary node 1 (6102) isillustrated in FIG. 61. Node 1 (6102) may include elements such as adirectional/omni antenna 6104, antenna controller 6106, a modem 6108,and a processor 6110. Exemplary node 1 (6102) may further include memory(not shown) in the form of volatile and/or nonvolatile memory such asread only memory (ROM) and random access memory (RAM). It will beappreciated by those skilled in the art that other types of computerreadable media that can store data that is accessible may be utilized.Furthermore, node 1 (6102) may be connected via Ethernet (6112) to anexternal network 6114.

FIG. 62 illustrates that exemplary node 1 (6102) may be connected toother nodes such as node 3 (6204), node 9 (6206), and node 11 (6208).Each of node 3 (6204), 9 (6206), and 11 (6208) may also have Ethernetconnections (6205, 6207, 6209) to enable allow each node to be connectedto other external networks.

The invention has been described with respect to specific examplesincluding various aspects of the invention. Those skilled in the artwill appreciate that there are numerous variations and permutations ofthe above described systems and techniques. Thus, the spirit and scopeof the invention should be construed broadly as set forth in theappended claims.

We claim:
 1. A method comprising: randomly selecting to transmit basedon a randomized choice between transmitting and receiving; transmittinga link establishment request from a node in response to the selection totransmit; receiving a link establishment response at the node; andupdating a steady-state schedule of the node for communication in a meshnetwork.
 2. The method of claim 1, further comprising pointing adirectional antenna to a bearing based on a function shared with othernodes of the mesh network, wherein the transmitting is from thedirectional antenna.
 3. The method of claim 2, further comprisingdetermining the bearing based on a time of day.
 4. The method of claim1, wherein the link establishment request transmitted by the nodeidentifies future available response frames.
 5. The method of claim 1,further comprising: in response to the receiving of the linkestablishment response, transmitting a bandwidth allocation responsewhich reserves particular frames of the steady-state schedule from amongunreserved idle frames for steady-state communication with a secondnode.
 6. The method of claim 1, wherein the steady-state scheduleindicates reserved communication opportunities of the node, and whereinthe updating of the steady-state schedule is based on communicationlinks between the node and other neighboring nodes in the mesh networkand based on the link establishment response.
 7. A method comprising:pointing a directional antenna of a node to a bearing synchronized withone or more other bearings of one or more other nodes of a mesh network;transmitting a link establishment request from the directional antenna;receiving a link establishment response; and updating a steady-stateschedule of the node for communication in the mesh network.
 8. Themethod of claim 7, further comprising: selecting the bearing based on atime reference shared with the one or more other nodes of the meshnetwork.
 9. The method of claim 7, wherein the steady-state scheduleindicates reserved communication opportunities of the node, and whereinthe updating of the steady-state schedule is based on communicationlinks between the node and neighboring nodes in the mesh network andbased on the link establishment response.
 10. A method comprising:determining a bearing; randomly selecting, based on a randomized choice,between transmitting from a node and receiving at the node acommunication to establish a link in a mesh network with one or moreother nodes; if transmitting the communication is selected, thentransmitting the communication from a directional antenna of the node ina direction of the bearing; and if receiving the communication isselected, then listening by the node for the communication from the oneor more other nodes.
 11. The method of claim 10, further comprising:determining a time for the transmitting or the receiving of thecommunication, wherein the bearing is the same for the node and the oneor more other nodes at the determined time.
 12. The method of claim 11,further comprising: updating the bearing to a new bearing according to apredetermined scan order.
 13. The method of claim 12, wherein thepredetermined scan order for updating the bearing depends on a time ofday.
 14. A non-transitory computer-readable medium havingcomputer-executable instructions stored thereon, that when executed by aprocessor, cause an apparatus containing the processor to: randomlyselect to transmit based on a randomized choice between transmitting andreceiving; transmit a link establishment request from the apparatus inresponse to the selection to transmit; receive a link establishmentresponse at the apparatus; and update a steady-state schedule of theapparatus for communication with one or more nodes in a mesh network.15. The non-transitory computer-readable medium of claim 14, wherein thecomputer-executable instructions, when executed by the processor,further cause the apparatus to: point a directional antenna to a bearingbased on a function shared with the one or more nodes in the meshnetwork, wherein the transmitting is from the directional antenna. 16.The non-transitory computer-readable medium of claim 14, wherein thelink establishment request transmitted by the apparatus identifiesfuture available response frames.
 17. The non-transitorycomputer-readable medium of claim 14, wherein the computer-executableinstructions, when executed by the processor, further cause theapparatus to: in response to receiving the link establishment response,transmit a bandwidth allocation response which reserves particularframes of the steady-state schedule from among unreserved idle framesfor steady-state communication with one of the one or more nodes. 18.The non-transitory computer-readable medium of claim 14, wherein thesteady-state schedule indicates reserved communication opportunities ofthe apparatus, and wherein the updating of the steady-state schedule isbased on communication links between the apparatus and neighboring nodesin the mesh network and based on the link establishment response.
 19. Anapparatus comprising: one or more antennae; a processor; and one or morememory having computer-executable instructions stored thereon, that whenexecuted by the processor, cause the apparatus to: randomly select totransmit based on a randomized choice between transmitting andreceiving; transmit a link establishment request from the one or moreantennae in response to the selection to transmit; receive a linkestablishment response on the one or more antennae; and update asteady-state schedule of the apparatus for communication in a meshnetwork.
 20. The apparatus of claim 19, wherein the one or more antennaeprovide sectorized reception.